Patterns of sexual and romantic behavior have changed significantly over the past half century. Sexual transition occurs earlier and outside of marriage, lifetime numbers of sexual partners have increased, and entry into marriage occurs later or not all. These behavioral and attitudinal changes have occurred in a context in which other developmental transitions and traditional sociological markers of adulthood are delayed. Embedded in these dramatic population changes are conflicting beliefs about optimal pathways to healthy sexuality and quality of life. Despite public policy emphasis on a pathway defined by abstinence until marriage, there is little prospective documentation of sexual trajectories from adolescence into adulthood or information about the enduring developmental and health implications, if any, of different sexual and romantic pathways. Using data from Waves I - IV of the National Longitudinal Study of Adolescent Health (Add Health), this project will: 1) examine trajectories defined by: I) timing, emergence of sexual acts, and temporal spacing; II) partner accumulation, frequency of activity and risk-taking (level and slope); and III) changes in indicators of sexual orientation over time; and determine whether trajectories vary by biological sex, race/ethnicity, or physical disability; 2) test hypotheses derived from Life Course and other developmental theory about how the interactions of biological characteristics, psychological factors, and life experiences sustain or change sexual and romantic trajectories across the life course; and 3) identify concurrent and later health correlates of trajectories, and where associations exist, test hypotheses about mediating mechanisms. Longitudinal analyses will include discrete hazard models, multiple decrement life table analysis, regression models for nonhomogeneous Poisson process to estimate individual-specific trajectories, multinomial logistic generalized linear mixed models, latent class growth models to cluster trajectories by type, multivariate transition models for sequencing and time between onset of different behaviors, and dual trajectory models to capture dynamic system interactions between change processes. Identifying trajectories of experience and their health implications for persons embedded in different cultural contexts will enrich developmental theory about diverse forms of positive development, and will provide empirical evidence based on representative samples to guide the development of public health policy and programs.